Sample Paper 02

Sample Paper – 2010Class – XIISubject – PhysicsBased on the new pattern for CBSE board examination 2010Time allowed: 3 hours Maximum Marks : 70General Instructions:All questions are compulsory.Question numbers 1 to 8 are very short answer type questions, carrying one mark each.Question numbers 9 to 18 are short answer type questions, carrying two marks each.Question numbers 19 to 27 are also short answer type questions, carrying three marks each.Question numbers 28 to 30 are long answer type questions, carrying five marks each.Use of calculators is not permitted. However, you may use log tables, if necessary.You may use the following physical constants wherever necessary :c = 3 x 108ms-1h = 6.6 x 10-34Jse = 1.6 x 10-19 Cμo = 4 π x 10−7T m A−1Boltzmann constant k = 1.38 x 1023 JK-1Avogadro’s number NA = 6.023 x 1023/moleMass of neutron mn = 1.6 x 10-27 kgMass of electron me = 9.1 x 10-31 kgWhich is preferred for the transmission of music -frequency modulation or amplitude modulation and why? 1Two semiconductor materials X and Y shown in the given figure are made by doping germanium crystal with arsenic and indium respectively. The two are joined end to end and connected to a battery as shown. Will the junction be forward biased or reverse biased? 1Four nuclei of an element fuse together to form a heavier nucleus. If the process is accompanied by release of energy, which of the two - the parent or the daughter nucleus would have a higher binding energy/nucleon? 1In a series LCR circuit, the voltages across an inductor, a capacitor and a resistor are 60 V, 60 V and 60V respectively. What is the phase difference between the applied voltage and the current in the circuit?1 Ultraviolet radiations of different frequencies 1 and 2 are incident on two photosensitive materials having work functions, Wl and W2 (Wl > W2) respectively. The maximum kinetic energy of the emitted electrons is same in both the cases. Which one of the two radiations will be of higher frequency? 1What is the angle between the directions of electric field at any (i) axial point and (ii) equatorial point due to an electric dipole? 1An electron is moving along +ve x-axis in the presence of uniform magnetic field along +ve y-axis. What is the direction of the force acting on it? 1What should be the length of dipole antenna, for a carrier wave of frequency 6 x 108 Hz? 1A galvanometer has a resistance of 30 ohm. It gives full scale deflection with a current of 2mA. Calculate the value of the resistance needed to convert it into an ammeter of range 0 - 0.3A. 2Calculate the current drawn by the primary of a transformer which steps down 400 V to 40 V to operate a device of resistance 20 .Assume the efficiency of the transformer to the 80%. 2An AC voltage of 100 V-50 Hz is connected across a 20 ohm resistor and 2mH inductor in series. Calculate the (i) impedance of the circuit, (ii) rms current in the circuit. 2 OR A capacitor and a resistor are connected in series with an AC source. If the potential difference across capacitor and resistor are 90 V and 120 V respectively, and if the rms current of the circuit is 3 A, calculate the (i) impedance of the circuit, (ii) power factor the circuit. 2Light of wavelength 550 nm. is incident as parallel beam on a slit of width 0.1mm. Find the angular width and the linear width of the principal maxima in the resulting diffraction pattern on a screen kept at a distance of 1.1m from the slit. Which of these widths would not change if the screen were moved to a distance of 2.2m from the slit? 2 Define resolving power of a compound microscope. How does the resolving power of a compound microscope change when:(i) refractive index of the medium between the object and objective lens increases?(ii) wavelength of the radiation used is increased? 2Explain the underlying principle of working of a parallel plate capacitor. 'If two similar plates, each of area A having surface charge densities + and - are separated by a distance d in air, write expressions for(i) the electric field at points between the two plates.(ii) the potential difference between the plates.(iii) the capacitance of the capacitor so formed. 2The number density of free electrons in a copper conductor is 8.5 x 1028 m-3. How long does an electron take to drift from one end of a wire 3.0 m long to its other end? The area of cross-section of the wire is 2.0 x 10-6 m2 and is carrying a current of 3.0 A. 2Draw the curve showing the variation of binding energy/nucleon with mass number of different nuclei. Briefly, state how nuclear fission and nuclear fusion can be explained on the basis of this graph. 2Keeping the voltage of the charging source constant, what would be the percentage change in the energy stored in a parallel plate capacitor if the separation between its plates were to be decreased by 10%? 2The following data was recorded for values of object distance and the corresponding values of image distance in the experiment on study of real image formation by a convex lens of power +5D. One of these observations is incorrect. Indentify this observation and give reason for your choice: 2S. No.123456Object Distance (cm)253035455055Image distance (cm)976137353230Define the term ‘Activity’ of a radioactive substance. State its SI unit. Two different radioactive elements with half lives T1 and T2 have N1 and N2 (undecayed) atoms respectively present at a given instant. Determine the ratio of their activities at this instant. 3 What is space wave propagation? Which two communication methods make use of this mode of propagation? If the sum of the heights of transmitting and receiving antennae in line of sight of communication is fixed at h, show that the range is maximum when the two antennae have a height each. 3Name the following constituent radiations of electromagnetic spectrum which(i) produce intense heating effect (wavelength λ1).(ii) is absorbed by the ozone layer in the atmosphere (wavelength λ2).(iii) is used for studying crystal structure (wavelength λ3). Name the characteristic of electromagnetic waves that increases in the electromagnetic spectrum as one moves from λ3 to λ1. 3Explain, with the help of a schematic diagram, the principle and working of a Light Emitting Diode. What criterion is kept in mind while choosing the semiconductor material for such a device? Write any two advantages of Light Emitting Diode over conventional incandescent lamps. 3Radiations of frequency 1015Hz are incident on two photosensitive surfaces X and Y. Following observations are recorded:Surface A: No photo-emission takes place.Surface B: Photo-emission takes place but photo-electrons have zero energy.Explain the above observations on the basis of Einstein's photo-electric equation. How will the observation with surface B change when the wavelength of incident radiations is decreased? 3Draw a labelled ray diagram of an astronomical telescope. Write mathematical expression for its magnifying power. How does the magnifying power get affected on increasing the aperture of the objective lens and why? 3State Gauss's theorem in electrostatics. Using it, deduce an expression for electric field intensity at a point near a thin infinite plane sheet of electric charge. 3Explain the term 'inductive reactance'. Show graphically the variation of inductive reactance with frequency of the applied alternating voltage. An a.c. voltage E =Eo sin t is applied across a pure inductor of inductance L. What will the current flowing through it?ORExplain the term 'capacitive reactance'. Show graphically the variation of capacitive reactance with frequency of the applied alternating voltage. An a.c. voltage E =Eo sin t is applied across a pure capacitor of capacitance C. What will the current flowing through it?What kind of a circuit arrangement should be used to study the input and output characteristics of a n-p-n silicon transistor in the Common Emitter configuration. Draw the typical shape of input and output characteristics likely to be obtained. 3State the essential condition for diffraction of light to take place. Use Huygens' principle to explain diffraction of light due to a narrow single slit and the formation of a pattern of fringes obtained on the screen. Sketch the pattern of fringes formed due to diffraction at a single slit showing variation of intensity with angle. 5OR(a) Draw a ray diagram to show the refraction of light through a glass prism. Hence obtain the relation for the angle of deviation in terms of the angle of incidence, angle of emergence and the angle of the prism.(b) A right angled isosceles glass prism is made from glass of refractive index 1.5. Show that a ray of light incident normally on(i) one of the equal sides of this prism is deviated through 900(ii) the hypotenuse of this prism is deviated through 1800 5State Ohm’s law. Two materials have different resistivities. Two wires of the same length are made, one from each of the materials. Is it possible for the two wires to have the same resistance? Explain.A 75.0 Ω and a 45.0 Ω resistor are connected in parallel. When this combination is connected across a battery, the current delivered by the battery is 0.294 A. What the 45.0 Ω resistor is disconnected, the current drops to 0.116 A. Determine (a) the emf and (b) internal resistance of the battery. 5ORThe variation of potential difference V with the length l of wire is plotted in the given figure for two potentiometers X and Y. Which one of the two potentiometers will you prefer for comparing emfs of cells and why?For the potentiometer circuit shown in the given figure, points X and Y represent the two terminals of an unknown emf E1. A student observed that when the jockey is moved from the end A to the end B of the potentiometer wire, the deflection in the galvanometer remains in the same direction.What may be the two possible faults in the circuit that could result in this observation?If the galvanometer deflection at the end B is (i) more, (ii) less, than that at the end A, which of the two faults, listed above, would be there in the circuit? . Give reasons in support of your answer in each case. 530. (i) Derive an expression for the magnetic field at a point on the axis of a current carrying circular loop.(ii) Two coaxial circular loops L1 and L2 of radii R1 = 3cm and R2 = 4cm are placed as shown. What should be the magnitude and direction of the current in the loop L2 so that the net magnetic field at the point O be zero?OR(i) What is the relationship between the current and the magnetic moment of a current carrying circular loop? Use the expression to derive the relation between the magnetic moment of an electron moving in a circle and its related angular momentum?(ii) A muon is a particle that has the same charge as an electron but is 200 times heavier than it. If we had an atom in which the muon revolves around a proton instead of an electron, what would be the magnetic moment of the muon in the ground state of such an atom?